The present invention relates to a method of driving a liquid crystal device using a simple matrix panel. The present invention also relates to a liquid crystal device and an electronic instrument using the liquid crystal device, such as OA equipment and measuring instruments.
In a liquid crystal device using a simple matrix panel, a method of changing a bias ratio according to the power supply voltage or a method of changing a bias ratio when changing a display duty has been employed. The display duty must be changed when changing from a full screen display to a partial display, for example.
In conventional liquid crystal devices, a maximum voltage in a liquid crystal driving voltage generated by raising the power supply voltage is divided using a resistance dividing circuit, thereby generating various levels of liquid crystal driving voltages.
The bias ratio must be changed when changing the display duty in order to maximize an operation margin. Conventionally, the resistance value of a resistance element in the resistance dividing circuit is designed to be variable. An electric current flowing through the resistance dividing circuit changes when changing the resistance value, whereby the levels of each liquid crystal driving voltage change. Therefore, conventional technology has a problem in that contrast must be adjusted each time the display duty is changed.
Accordingly, an object of the present invention is to provide a method of driving a liquid crystal device which can eliminate the need for adjustment of contrast by the user when changing the display duty, a liquid crystal device, and an electronic instrument.
Another object of the present invention is to provide a method of driving a liquid crystal device which can easily display a partial display and which enables a partial display with low power consumption, a liquid crystal device, and an electronic instrument.
One aspect of the present invention provides, a method of driving a liquid crystal device comprising a first substrate on which a plurality of electrodes are formed, a second substrate on which a plurality of segment electrodes are formed, and a liquid crystal interposed between the first substrate and the second substrate, and applying a voltage which changes into at least an ON voltage and an OFF voltage to a pixel formed at each intersection point of the common electrodes and the segment electrodes, the method comprising:
a first driving step of driving the liquid crystal device under a condition of a first duty and a first bias ratio; and
a second driving step of driving the liquid crystal device under a condition of a second duty and a second bias ratio,
wherein the first duty and the second duty and the first bias ratio and the second bias ratio are set so that a root-mean-square voltage applied to the pixel when the intermediate voltage between the ON voltage and the OFF voltage is applied to the pixel in the first driving step equals a root-mean-square voltage applied to the pixel when the intermediate voltage between the ON voltage and the OFF voltage is applied to the pixel in the second driving step.
According to this aspect of the present invention, the bias ratio is changed when changing the display duty so that the intermediate values between the ON voltage and the OFF voltage are almost equal. This allows the medium concentration to be almost constant before and after changing the duty. Therefore, the user does not have to adjust the contrast each time the duty is changed.
This aspect of the present invention can be applied to both one-line selection driving and multi-line driving.
Another aspect of the present invention provides, a method of driving a liquid crystal device comprising a first substrate on which a plurality of electrodes are formed, a second substrate on which a plurality of segment electrodes are formed, and a liquid crystal interposed between the first substrate and the second substrate, and applying a voltage which changes into at least an ON voltage and an OFF voltage to a pixel formed at each intersection point of the common electrodes and the segment electrodes, the method comprising:
a first driving step of driving the liquid crystal device under a condition of a first duty n1 and a first bias ratio c1; and
a second driving step of driving the liquid crystal device under a condition of a second duty n2 and a second bias ratio c2,
wherein the first duty and the second duty and the first bias ratio and the second bias ratio are set to satisfy n1xe2x88x92c12=n2xc2x7c22.
According to this other aspect, the bias ratio is changed from c1 to c2 when changing the display duty from n1 to n2 so that the intermediate values between the ON voltage and the OFF voltage are almost equal. The condition required for this is to satisfy the relation n1xc2x7c12=n2xc2x7c22 according to a Ruckmongathan""s equation as described later. This aspect can be applied to both one-line selection driving and multi-line driving.
The first driving step may comprise a step of raising a maximum signal potential supplied to the segment electrodes to generate a selection potential to be supplied to the common electrodes. The second driving step may comprise a step of stopping the raising step and supplying the maximum signal potential supplied to the segment electrodes to the common electrodes as the selection potential.
This configuration allows the raising operation can be stopped in the second driving step, thereby reducing power consumption. Moreover, since the potential for the segment electrodes is supplied to the common electrodes, there is no need to generate other liquid crystal drive potentials.
When a voltage-raising multiplying factor is xe2x80x9ckxe2x80x9d in the raising step performed in the first driving step, the relation n2=n1xc2x7(1/k)2 may be realized. This is because the bias ratios n1 and n2 and the voltage-raising multiplying factor xe2x80x9ckxe2x80x9d in the raising step satisfy the relation c1/c2=1/k.
A further aspect of the present invention provides, a method of driving a liquid crystal device comprising a first substrate on which a plurality of electrodes are formed, a second substrate on which a plurality of segment electrodes are formed, and a liquid crystal interposed between the first substrate and the second substrate, and applying a voltage which changes into at least an ON voltage and an OFF voltage to a pixel formed at each intersection point of the common electrodes and the segment electrodes, the method comprising:
a first driving step of driving the liquid crystal device under a condition of a first duty and a first bias ratio; and
a second driving step of driving the liquid crystal device under a condition of a second duty lower than the first duty and a second bias ratio,
wherein the first duty and the second duty and the first bias ratio and the second bias ratio are set so that a root-mean-square voltage applied to the pixel when the ON voltage is applied to the pixel in the first driving step is equal to or less than a root-mean-square voltage applied to the pixel when the ON voltage is applied to the pixel in the second step, and a root-mean-square voltage applied to the pixel when the OFF voltage is applied to the pixel in the first driving step is equal to or more than a root-mean-square voltage applied to the pixel when the OFF voltage is applied to the pixel in the second step.
According to this further aspect of the present invention, the bias ratios are selectively changed so that the range between the ON voltage and the OFF voltage at a high duty (first duty) includes the range between the ON voltage and the OFF voltage at a low duty (second duty). This allows the contrast obtained in the low-duty driving to be higher than the contrast obtained in the high-duty driving Therefore, the user does not have to adjust the contrast each time the display duty is changed. This aspect can be applied to both one-line selection driving and multi-line driving.
A liquid crystal device according to a still further aspect of the present invention comprises;
a panel including a first substrate on which a plurality of electrodes are formed, a second substrate on which a plurality of segment electrodes are formed, and a liquid crystal interposed between the first substrate and the second substrate;
a segment driver which supplies a voltage to the segment electrodes;
a common driver which supplies a voltage to the common electrodes; and
a power supply circuit which supplies a liquid crystal driving voltage to the common driver and the segment driver,
wherein the segment driver includes a circuit of which duty changes between a first duty n1 and a second duty n2 (n2 less than n1),
wherein the power supply circuit comprises a circuit which sets a bias ratio at a first bias ratio c1 when the first duty n1 is set, and sets a bias ratio at a second bias ratio c2 when the first duty n2 (c2 greater than c1) is set, and
wherein the first duty and the second duty and the first bias ratio and the second bias ratio are set to satisfy n1xc2x7c12=n2xc2x7c22.
The drive method according the above-described other aspect of the present invention is suitably applied to this liquid crystal device.
In addition, the common driver and the power supply circuit may be included in a single-chip IC.
An electronic instrument according to still another aspect of the present invention has the above-described liquid crystal device. The liquid crystal device used as a display for the electronic instrument may be driven at a high duty during a normal operation mode, and driven at a low duty when displaying a partial display during a wait mode. In the case of a portable telephone, in particular, power consumption can be reduced by displaying an icon or the like on only part of the display screen in a wait mode without displaying in other areas. The electronic instrument according to the present invention can be applied to any type of electronic instrument which requires partial display in the low-duty driving. The electronic instrument is particularly suitable as a mobile apparatus for which low power consumption is needed.